1. Field of the Invention
The present invention relates to an apparatus and method, particularly, but not exclusively, for use with increasing the speed of tripping into or out of a subsea well on a floating production platform or vessel used in the exploration, exploitation and production of hydrocarbons. Particularly, the apparatus and method is for use in workovers, well maintenance and well intervention in subsea wells, but could also relate to other uses such as water exploration, exploitation and production.
2. Description of the Related Art
Conventional drilling operations for hydrocarbon exploration, exploitation and production utilize many lengths of individual tubulars (or OCTG products) which are made up into a string, where the tubulars are connected to one another by means of screw threaded couplings provided at each end. Various operations require strings of different tubulars, such as drillpipe, casing and production tubing. The individual tubular sections are made up into the required string on the drilling rig or floating production vessel, etc., by inserting them into the subsea surface well through a riser which extends from the subsea surface up to the drilling rig. A make up/breakout unit adds or removes an individual tubular section from the required string. Conventionally, this is a relatively time consuming task, since the string must be held in conventional slips located on the drilling rig whilst e.g. a new tubular is included in the top of the string on the drilling rig. In addition, conventional drilling rigs, such as jack ups, floating drilling rigs and drill ships are relatively expensive both in terms of manpower and rental rates which may be in the region of 100 men and U.S.$200,000 per day respectively.
According to a first aspect of the present invention there is provided an apparatus for inserting or removing a string of tubulars from a sub-sea borehole, the apparatus comprising:
a first, lower, gripping mechanism located subsea in the vicinity of the subsea borehole, the first gripping mechanism being capable of gripping a portion of the string of tubulars;
a second, upper, gripping mechanism located subsea in the vicinity of the subsea borehole, the second gripping mechanism being capable of gripping a portion of the string of tubulars;
wherein the first and second gripping mechanisms are moveable with respect to one another; and
a movement mechanism which, when actuated, moves one of the first and second gripping mechanisms with respect to the other of the first and second gripping mechanisms, such that the string of tubulars is inserted into or removed from the subsea borehole.
According to a second aspect of the present invention there is provided a method of inserting or removing a string of tubulars from a sub-sea borehole, the method comprising:
providing a first gripping mechanism subsea in the vicinity of the subsea borehole, the first gripping mechanism being capable of gripping a portion of the string of tubulars;
providing a second gripping mechanism located subsea in the vicinity of the subsea borehole, the second gripping mechanism being capable of gripping a portion of the string of tubulars;
wherein the first and second gripping mechanisms are moveable with respect to one another;
providing a movement mechanism which is capable of moving one of the first and second gripping mechanisms with respect to the other of the first and second gripping mechanisms; and
actuating the movement mechanism such that the string of tubulars is inserted into, or removed from, the subsea borehole.
Preferably, the first gripping mechanism is lower than the second gripping mechanism, and more preferably, the first gripping mechanism is substantially stationary with respect to the mouth of the subsea borehole, and the second, upper, gripping mechanism is moved with respect to the first gripping mechanism.
Typically, the second, upper, gripping mechanism is operated to grip the string of tubulars whilst the movement mechanism is actuated, and when this is the case, the first, lower, gripping mechanism is preferably not actuated such that the first, lower, gripping mechanism does not grip the string of tubulars.
Preferably, the first, lower, gripping mechanism is operated to grip the string of tubulars when the second, upper, gripping mechanism is not operated to grip the string of tubulars.
Typically, the movement mechanism comprises a jacking mechanism including a piston cylinder and a piston located within the piston cylinder, wherein one of the first and second gripping mechanisms is secured to the piston and the other of the first and second gripping mechanisms is secured to the piston cylinder. Preferably, the jacking mechanism is operated by introducing fluid into, or removing fluid from, one side of the piston within the piston cylinder. Preferably, a fluid reservoir, which is preferably a high pressure fluid reservoir, is provided to introduce fluid into, or remove fluid from, one side of the piston within the piston cylinder, and more preferably, the fluid reservoir is located subsea, typically in close proximity to the jacking mechanism.
Preferably, the jacking mechanism and first and second gripping means are all located vertically above, and typically in line with, a subsea equipment package which includes at least a subsea blow-out preventor (BOP).
Preferably, there is further provided a make up/break out mechanism which is capable of adding a tubular to or removing a tubular from the string. Typically, there is further provided a handling mechanism which is adapted to deliver a tubular into, or remove a tubular from, the make up/break out mechanism. Preferably, the make up/break out mechanism, and typically the handling mechanism is/are located on a vessel at the sea surface, where the vessel is typically located substantially vertically above the apparatus located subsea. Typically, a compensation mechanism is provided to compensate the make up/break out mechanism for movement of the vessel in the sea, typically in a direction parallel to the axial direction of the string, such that the string may be substantially continuously inserted into or removed from the borehole.
Typically, the make up/breakout mechanism further comprises a pair of vertically spaced tongs which are adapted to selectively grip the tubulars. More preferably, the uppermost tong is adapted to impart rotation to a tubular.
Typically, a riser is further provided into an upper end of which the string is inserted into at the vessel. The lower end of the riser may be sealed with respect to the sea or may be open with respect to the sea.
A control system is preferably provided to control actuation of the first and second gripping mechanisms and preferably also the jacking mechanisms. Typically, the fluid reservoir is charged up from a pump located on the vessel.